Pseudoelastic behaviour of a natural material is achieved via reversible changes in protein backbone conformation

Abstract

The egg capsules of marine prosobranch gastropods, commonly know as whelks, function as a protective encapsulant for whelk embryos in wave-swept marine environments. The proteinaceous sheets comprising the wall of whelk egg capsules (WEC) exhibit long-range reversible extensibility with a hysteresis of up to 50 per cent, previously suggested to result from reversible changes in the structure of the constituent protein building blocks. Here, we further investigate the structural changes of the WEC biopolymer at various hierarchical levels using several different time-resolved in situ approaches. We find strong evidence in these biological polymers for a strain-induced reversible transition from an ordered conformational phase to a largely disordered one that leads to the characteristic reversible hysteretic behaviour, which is reminiscent of the pseudoelastic behaviour in some metallic alloys. On the basis of these results, we generate a simple numerical model incorporating a worm-like chain equation to explain the phase transition behaviour of the WEC at the molecular level.

Mechanoresponsive lipid-protein nanoglobules facilitate reversible fibre formation in velvet worm slime

“…3d, e). More ambiguous are sharp bands centred at 1649 and 1324 cm −1 that could indicate either C = C stretching and CH 2 twisting vibrations of lipid molecules 24 or amide I and amide III bands of α-helical proteins 25, 26 , respectively. However, considering that slime proteins were previously reported to be highly unstructured 11 and because lipid =C-H stretching (3010 cm −1 ) is typically accompanied by a complementary peak around 1650 cm −1 , we assign these peaks to lipid vibrations 24, 27 (Supplementary Fig.…”

Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration

“…Recent studies on whelk egg capsules, which also show the a-helix ? b-sheet transition that is reversible (detailed in Section 3.1.9), have found that the process is driven more by internal energy than entropy changes [116,173].…”

An energetic model for macromolecules unfolding in stretching experiments

“…The past decade has shown a significant theoretical and experimental effort in the analysis of the thermomechanical behaviour of macromolecular materials such as muscle tissues [1], spider silks [2,3], polymers and biopolymers [4], polysoaps [5,6] and silks in general [7]. A common property of these materials [2,4,[8][9][10] is that their macroscopic history-dependent, dissipative response is the result of complex evolutions of 'semicrystalline' microstructures.…”

“…A common property of these materials [2,4,[8][9][10] is that their macroscopic history-dependent, dissipative response is the result of complex evolutions of 'semicrystalline' microstructures. These are constituted by flexible (polymeric or protein) macromolecules reinforced by strong and stiff crystals (e.g.…”